Impact of motor activity and antennal mechanosensory input on the intensity of proctolin-like immunoreactivity in antennal motoneurons of crickets ( Gryllus bimaculatus )

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The change of the intensity of proctolin immunolabeling of 2 of 17 proctolinergic antennal motoneurons [one adductor (Ad3), and one depressor (D5)] was quantitatively studied in crickets in relation to flight and antennal deafferentation. During flight, the maintained forward position of the antennae is supported by high frequency tonic firing of Ad3 but probably all motoneurons are activated. In animals sacrificed immediately after the last of five consecutive flight periods the intensity of proctolin-like immunolabeling showed a significant decrease in the Ad3 soma in comparison to the Ad3 of non-flyers. The identical result was observed in the D5 soma. In animals sacrificed 40 h after flight, no difference in the intensity of proctolin immunolabeling between the Ad3 soma of flyers and non-flyers was evident. Thus, at high motoneuron activity, the production of proctolin may not be able to keep pace with its transport from the soma. Deletion of all proprioceptors of one antenna which respond to horizontal movements only led to a significant decrease of the intensity of proctolin immunolabeling in the Ad3 soma on the operated side, but not in the soma of D5. This indicates that selected afferent input has an impact on proctolin expression in distinct motoneuron pools.